I regret opening contract with mtn

Mtn contract didnt debit the money on the 7th then on the 8th they debited it,Tuesday morning they sent the money back saying payment failed,I then paid the money again through EFT on my app on this account MTN worldwide advisory *** from my FNB ***,also sent proof of payment,

and I got an email that the money didnt reflect I must contact my bank,but when checked the money did reflect to FNB mtn advisory,today I get a call that I must pay R456 instead of R308 I usually pay monthly,I did sent several emails and no one answered me,I wanted mtn to send back my money so that I can pay it where I was suppose to pay it.now I just called mtn advisory the guy just took my number and ID no and said he will call ne back which I know he was lying..What is wrong with mtn,no ways they ****ming people,instead sending you the money you sent so you can send it to the correct account they later gave you they increase the payment which is totally wrong.